Don't compare full executed block to determine whether there was a conflict.

[afck]

With #3164, the execution outcome can depend on the current round.

If this oracle is used, we shouldn't try to discern ExecuteBlockOutcome::Executed from ExecuteBlockOutcome::Conflict by comparing the exact executed block.

One alternative is to check that the ProposedBlock matches (i.e. the operations and messages are the ones we were meaning to commit) and that we are the block's signer. (#456 might be a prerequisite for doing that.)